Cells- Cell Cycle And Cancer

Question 1

When a cell is not dividing, what form is the DNA in?

Answer 1

The DNA is in the form of CHROMATIN

Chromatin is uncoiled and thread-like.

Question 2

What happens to the DNA when a cell is about to divide?

Answer 2

The chromatin CONDENSES to form CHROMOSOMES

Chromosomes are shorter, coiled DNA in rod-like structures.

Question 3

What do we mean by the DIPLOID number?

Answer 3

The diploid number refers to chromosomes arranged as HOMOLOGOUS PAIRS; specifically 23 pairs in humans, written as 2n = 46

This indicates two sets of chromosomes.

Question 4

What do we mean by the HAPLOID number?

Answer 4

The haploid number refers to the presence of only one chromosome from each homologous pair; in humans, this is true of the sex cells, written as n = 23

Haploid cells contain half the number of chromosomes.

Question 5

What do we mean by the ‘karyotype’ of an organism?

Answer 5

The karyotype is the number, appearance and arrangement of the homologous chromosome pairs

It provides a visual representation of the organism’s chromosomes.

Question 6

What are ‘histones’ and ‘nucleosomes’?

Answer 6

Histones are proteins that support DNA; nucleosomes are made from stacks of histones around which the DNA is coiled

Nucleosomes help in packaging DNA into a compact form.

Question 7

What is a HOMOLOGOUS PAIR of chromosomes?

Answer 7

A homologous pair is where each chromosome carries genes along their length, at the same loci

They are similar in shape, size, and genetic content.

Question 8

What does the ‘cell cycle’ represent?

Answer 8

The cell cycle represents the entire life of a diploid cell, including G1, S, G2 (Interphase), mitosis, and cytokinesis

It describes the stages a cell goes through from division to division.

Question 9

What does interphase consist of?

Answer 9

Interphase consists of growth phase one (G1), synthesis phase (S), and growth phase two (G2)

Interphase is the phase where the cell prepares for division.

Question 10

What is the G1 phase?

Answer 10

G1 is the first growth phase of the cell cycle

It involves cell growth and preparation for DNA replication.

Question 11

What are the key events during G1?

Answer 11

Synthesis of new macromolecules including proteins and nucleotides, organelles are produced, cell increases in size, DNA synthesis occurs resulting in each chromosome consisting of 2 sister chromatids, histones are produced, synthesis of spindle proteins, chromosomes are checked for errors, energy stores are increased.

Question 12

What happens in S phase?

Answer 12

•DNA synthesis (by semi-conservative replication) occurs, resulting in each chromosome now consisting of 2 sister chromatids
•Histones are produced

Question 13

What are the key events in G2?

Answer 13

Cell continues to increase in size, checks for DNA replication accuracy, prepares for mitosis.

Question 14

Overall, what happens during mitosis?

Answer 14

Nuclear division, copying of chromosomes, division between two identical daughter cells.

Question 15

What are the four stages of mitosis?

Answer 15

Prophase, Metaphase, Anaphase, Telophase.

Question 16

What is cytokinesis?

Answer 16

The division of the cell into 2 separate daughter cells at the end of mitosis.

Question 17

Why are checkpoints needed in the cell cycle?

Answer 17

They regulate the cycle by checking and monitoring each stage to ensure that no errors have occurred before the process continues.

Question 18

Where are the main checkpoints in the cell cycle?

Answer 18

1. End of G1, before S phase
   For nutrient levels, DNA damage, check on growth factors
2. End of G2, before mitosis.
   Check on cell size and that DNA replication has occurred correctly
3. During the metaphase stage of mitosis (check that spindle fibres are attached properly to chromosomes)

Question 19

What does the G1 checkpoint check for?

Answer 19

Nutrient levels, DNA damage, growth factors.

Question 20

What does the G2 checkpoint check for?

Answer 20

Cell size, accuracy of DNA replication.

Question 21

What is the Go phase?

Answer 21

Resting state of the cell.

Question 22

What does the metaphase checkpoint check for?

Answer 22

Checks that spindle fibres are attached properly to chromosomes

Question 23

What is Go?

Answer 23

A resting state of the cell cycle where a cell is not actively dividing

Cells in Go may carry out normal cellular activities or remain inactive until triggered to re-enter the cell cycle.

Question 24

What occurs in Go?

Answer 24

Cells are in a resting state and may carry out normal cellular activities or remain inactive

Some cells may return to the cell cycle when triggered.

Question 25

What does the G2 checkpoint ensure before a cell can start mitosis?

Answer 25

That DNA replication is accurate and there is no DNA damage ## Footnote This checkpoint is crucial for preventing mutations and ensuring proper cell division.

Question 26

What causes cancer?

Answer 26

Uncontrolled cell division (mitosis) due to failure of the regulation mechanism at the checkpoints ## Footnote Cancer cells fail to enter Go when they should, leading to continuous division.

Question 27

What is chemotherapy?

Answer 27

Using drugs to treat cancer, normally by disrupting the cell cycle and mitosis ## Footnote Chemotherapy aims to stop cancer cell proliferation.

Question 28

How do mitotic poisons work in chemotherapy?

Answer 28

They inhibit formation of spindle fibre microtubules, preventing anaphase from occurring ## Footnote Example: Vincristine.

Question 29

How do antimetabolites work in chemotherapy?

Answer 29

They inhibit S-Phase and therefore DNA replication/synthesis ## Footnote Example: Fluorouracil.

Question 30

Fill in the blank: If a cell fails at the _______ checkpoint, it enters Go or the 'resting state' until it is ready to enter S phase.

Answer 30

ol